Sortilin (also called NTR-3 or GP95) is a type I membrane receptor belonging to the Vps10p (vacuolar protein sorting 10 protein) domain family of sorting receptors (Winnow et al, Nat Rev Neurosci, 12:899-909 (2008)) which also comprises SorLA, SorCS1, SorCS2 and SorCS3. The Vps10p family shares the Vps10p extracellular domain of approximately 700 amino acids, originally identified as a sorting receptor in Saccharomyces cerevisiae, which in sortilin encompasses the entire extracellular part forming a so-called 10-bladed beta-propeller, the structure of which has been reported (Quistgaard et al, Nat Struct Mol Biol, 1:96-8 (2009)). Sortilin is widely expressed in the peripheral and central nervous system in neurons as well as in other tissues and cells including liver, heart, testis, uterus, kidney, skeletal muscle, T-cells, B-cells and NK cells (Petersen et al., J. Biol. Chem., 272:3599-3605 (1997); Herman-Borgmeyer et al., Mol. Brain Res., 65:216-219 (1999)). Herda et al, Immunity, 37(5):854-66 (2012)). Only a small fraction of the protein is expressed at the cell surface while an estimated 90% is localized intracellularly although the distribution for sortilin may be regulated by ligand interactions.
Sortilin has been shown to mediate pro-apoptotic effects of pro-neurotrophins, including pro-NGF, proNT3 and pro-BDNF which, through binding to a Sortilin-P75 complex, induce degeneration and cell death in cellular and animal models of a number of neurodegenerative disorders (Nykjaer et al, Nature, 427(6977):843-8 (2004)). In addition, sortilin mediates trafficking and sorting of neurotrophin receptors and also is a regulator of proBDNF secretion (Evans et al, J Biol Chem, 86(34):29556-67 (2011)). Thereby, sortilin is considered a key regulator of the balance between generally opposing effects of mature and pro-forms of neurotrophins Targeting sortilin-P75-mediated apoptosis has been suggested as a protective mechanism in neurodegenerative disorders based on studies in cellular and animal models related to acute and chronic neurodegenerative conditions. Specifically, sortilin has been suggested to have beneficial effects in pain as sortilin knockout mice were found to be protected in a spared nerve injury pain model (Nykjaer et al, WO 2009/155932 A2).
Several binding partners for sortilin have been identified in addition to pro-neurotrophins Sortilin has been shown to be a receptor for the neuropeptide neurotensin (Mazella et al, J Biol Chem., 273(41):26273-6 (1998)), and more recently also to function as a receptor for progranulin (PGRN) (Hu et al, Neuron, 68(4):654-67, (2010), Carrasquillo et al, Am J Hum Genet, 87(6):890-7 (2010)). The binding sites of neurotensin and progranulin have been characterized and shown to localize to the same amino acids (Hu et al, Neuron, 68(4):654-67, (2010), Quistgaard et al, Nat Struct Mol Biol, 1:96-8 (2009), Zheng et al, PLoS One. 2011; 6(6):e21023 (2011)) whereas the pro-neurotrophin binding site has been suggested to localize to a separate site from the neurotensin binding site (Senip Andersen et al, J Biol Chem. 285(16):12210-22 (2010)) although pro-neurotrophin binding is inhibited by neurotensin in functional tests.
Recently, sortilin has been shown to mediate clearance of PGRN by binding followed by cellular uptake and distribution to lysosomes. PGRN has neurotrophic properties and has been linked to frontotemporal lobar degeneration (FTLD), a neurodegenerative disorder characterized by inclusions positive for the RNA binding protein TAR DNA-binding protein 43 (TDP-43). In a subset of FTLD patients, PGRN expression is decreased due to mutations in the GRN gene. In mice, sortilin knock out was reported to increase PGRN levels and sortilin deficiency in PGRN+/−mice was found to increase PGRN to at least WT level. Therefore, targeting of sortilin has been suggested to alleviate or normalize PGRN expression levels to halt or slow neurodegeneration in FTLD (Prudencio et al, Proc Natl Acad Sci USA. 109(52):21510-5 (2012)). A genome-wide screening associated an SNP near the SORT1 gene locus with PGRN expression levels and furthermore, a study of altered expression and splicing after reducing TDP-43 in mouse brain by means of antisense oligonucleotides identified sortilin as being among the several alternatively spliced genes supporting a role for sortilin in ALS and TSDP-43 pathology (Polymenidou et al, Nat Neurosci. 14(4):459-68 (2011), Carrasquillo et al, Am J Hum Genet.; 87(6):890-7 (2010)).
In addition to TDP-43-pathology, PGRN has been attributed to other functions, including in inflammation and tissue repair. PGRN has been reported to bind TNF receptors with high affinity (Tang et al, Science, 332(6028):478-84 (2011)) thereby modulating TNF-alpha binding and showing proinflammatory effect in mouse models of rheumatoid arthritis. Therefore, targeting of sortilin has been suggested to exert anti-inflammatory effects by inhibiting PGRN clearance (Nykjaer and Willnow, Trends Neurosci., 35(4):261-70 (2012))
Sortilin is expressed in immune cells and has been implicated in inflammatory disorders as loss of sortilin was recently reported to reduce IFN-gamma release from CTL and TH1 T-cells and NK cells. It was suggested that sortilin modulates the adaptive and innate immune responses by regulating IFN-gamma secretion and that sortilin may be a target (Herda et al, Immunity, 37(5):854-66 (2012)) in inflammatory bowel disease and other IFN-gamma-dependent inflammatory disorders.
A number of other binding partners for sortilin have been reported. The growth factor CNTF was shown to bind sortilin with high affinity and to be cleared by cellular uptake (Larsen et al, Mol Cell Biol. (17):4175-87 (2010)) whereby sortilin modulated signalling through the GP103/LIFRbeta receptor complex, presumably via a direct interaction with LIFRbeta. A similar effect was observed for the related cytokines CT-1, LIF, OSM, and IL-6. Sortilin therefore is suggested to facilitate LIFRbeta-dependent signalling such that modulation of sortilin may be of benefit in disorders in which CNTF and related cytokines are of importance. Also, sortilin has been reported to mediate internalization of the kappa opioid receptor (Liu-Chen, 2012, poster, Society for Neuroscience annual meeting, 2012) and a peptide, spadin, which is cleaved of from pro-sortilin has been reported to bind TREK-1 potassium channels (Mazella et al, PLoS Biol. 8(4): e1000355, (2010)).
In addition, Sortilin is a major constituent of glucose transporter 4-containing vesicles (Morris et al, J Biol Chem. 273(6):3582-7 (1998)) and is believed to be involved as a cargo adaptor protein in the formation of the intracellular insulin responsive vesicles from the trans-Golgi network (Bogan et al, Curr Opin Cell Biol. (4):506-12 (2010)). Intracellularly, sortilin interacts with Apolipoprotein B100 (apoB100, Kjolby et al, Cell Metab, 12(3):213-23 (2010)). Recently, sortilin-apoB100 interaction was reported to be stimulated by insulin (Chamberlain, Biochem Biophys Res Commun. 50006-291X(12)02182-1 (2012) Epub ahead of print). Sortilin is also involved in the trafficking of prosaposin, acid sphingomye-linase and Cathepsin H and D to lysosomes. Sortilin was recently reported to bind APOE, a major risk factor in Alzheimers Disease as well as to soluble APP in primary hippocampal neurons (Carlo et al, J Neurosci, 33(1):358-70 (2013); Gustafsen et al, J Neurosci, 33(1):64-71 (2013)).
Gene polymorphisms on chromosome 1p13 have linked Sortl with metabolism of low density lipoprotein (LDL) cholesterol and risk of myocardial infarction or coronary artery disease in human patients (Linsel-Nitschke et al, Atherosclerosis., 208(1):183-9 (2010), Musunuru et al, Nature, 466(7307):714-9 (2010)). In one study, increased expression of sortilin associated with the polymorphism rs599839 was found to be correlated with lower levels of plasma LDL-cholesterol and decreased risk of coronary artery disease (Linsel-Nitschke et al, Atherosclerosis., 208(1):183-9 (2010)). However, other studies suggested that absence of sortilin resulted in decreased plasma cholesterol levels and in decreased plaque formation in aorta in mice deficient for the LDL receptor (Kjolby et al, Cell Metab, 12(3):213-23 (2010))). Thus, the mechanism linking sortilin to LDL metabolism and the net effect of altered sortilin expression is still a matter of debate (Dube et al, Bioessays., 33(6):430-7 (2011), Strong et al, Curr Atheroscler Rep., 14(3):211-8 (2012)) although there is agreement that sortilin associates with levels of circulating cholesterol/LDL and that modulation of sortilin function may represent a strategy to reduce levels of circulating LDL and alleviate cardiovascular risk.
Due to studies associating sortilin function with disease and the binding of sortilin to several proteins implicated in pathologies in the central nervous system as well as in the periphery, sortilin may represent an attractive therapeutic target. However, although the binding site of the sortilin ligands neurotensin and progranulin has been identified, no specific small molecule modulator of sortilin function has been disclosed to date.
The present invention aims at providing compounds which are inhibitors of sortilin and as such useful in the treatment of diseases associated with sortilin.